A disadvantage of this approach is that the locking of the rotor can only be accomplished with a plurality of successively locking pins, which results in higher costs. Further, the locking operation requires that the locking pins reliably lock successively. If one of the locking pins does not lock, the locking operation may be interrupted because the rotor is consequently not unidirectionally locked in the intermediate position and may rotate back.
It is an object of the present invention to provide a camshaft phaser having reliable and inexpensive means for locking the rotor in a central position.
In accordance with the fundamental idea underlying the present invention, it is proposed that one or more of the vanes altogether have at least two pressure medium conduits provided therein which each fluidically connect two working chambers of different directions of action, the at least two pressure medium conduits having provided therein respective check valves of different directions of action which each allow the pressure medium to be transferred between the working chambers in one direction and prevent it from being transferred in the respective opposite direction, depending on the direction of rotation of the rotor relative to the stator, and that at least one switchable valve device be provided in the rotor hub, the at least one switchable valve device in one operating position allowing the working chambers between which transfer of pressure medium is prevented by the check valve or between which no check valve is provided to be fluidically connected to each other.
The solution proposed herein allows the rotor to rotate in one direction relative to the stator utilizing the alternating torques (Camshaft Torque Actuated, CTA) acting on the camshaft during the starting phase of the internal combustion engine, while rotation in the respective other direction is blocked by the respective check valve. In this way, a kind a freewheel device is implemented, which enables the rotor to automatically rotate from an advance or retard stop position toward the central locking position until it is finally locked in the central locking position. In order to prevent the movement of the rotor from being impeded at the same time by the pressure medium in the working chambers between which no check valve is provided that acts in the same direction, these working chambers are short-circuited by the switchable valve device that is provided. The switchable valve device is deliberately disposed in the rotor hub, so that the working chambers can be short-circuited by a single valve device and a suitable conduit system including a plurality of pressure medium conduits in the rotor.
It is also proposed that the working chamber into which the pressure medium flows via the check valve be fluidically decoupled from the pressure medium circuit by the switchable valve device. If the pressure medium can flow into a plurality of working chambers via a plurality of check valves acting in the same direction, then, of course, all of these working chambers are decoupled from the pressure medium circuit. In order to decouple the working chamber, the valve device closes off a pressure medium conduit opening into the working chamber, thereby preventing the pressure medium from flowing out of the working chamber. The solution proposed herein also prevents the ability of the rotor, after a rotational movement in one direction, to rotate back in the respective other direction. In this way, the freewheel function already provided by the check valve is further assisted by the ability of the rotor to support itself against the stator via the vane and the pressure medium contained in the closed-off working chamber.
Further, it is proposed that one of the vanes have provided therein two pressure medium conduits which each have a check valve and enable the pressure medium to be transferred between the working chambers in different directions. The solution proposed herein makes it possible to further reduce the design complexity, the pressure medium in this case being blocked from flowing out of one or the other of the working chambers, depending on the return movement of the rotor. In this way, the freewheel function is implemented at one vane and two opposite working chambers alone.
It is further proposed that the working chambers of different directions of action be fluidically separated from each other by the switchable valve device when the rotor is in the central locking position. The connection of the pressure chambers via the switchable valve device and the transfer of pressure medium via the check valves serve solely for the purpose of for locking the rotor in a central position. To be able to subsequently adjust the phase angle of the camshaft relative to the crankshaft with the desired accuracy, the working chambers have to be fluidically separated again. In this connection, transfer of pressure medium via the check valves is acceptable within narrow limits, because, in this case, the rotor phasing accuracy is ensured by the working chambers that are pressurizable with pressure medium and have no check valve disposed therebetween.
In accordance with another preferred embodiment of the present invention, it is proposed that the first switchable valve device include at least two spring-loaded linearly displaceable locking pins of the central-position locking device. The linearly movable locking pins serve to lock the rotor, for example, in a locking slot that is provided in the cover of the camshaft phaser and is stationary with respect to the stator. In order to lock the rotor, the linearly movable locking pins necessarily execute a displacement movement which is here at the same time used to actuate the freewheel device; i.e., to fluidically couple and decouple the working chambers. Since the displacement movement of the locking pin at the same time causes the locking of the rotor relative to the stator, the switching instant of the valve device always coincides with the instant of locking, which makes it possible to achieve a very simple and also highly accurate control of the first valve device.
In this case, it is further proposed that the locking pins each be disposed between two sections of a pressure medium conduit and have grooves or bores via which the sections of the pressure medium conduit are fluidically connectable to each other, depending on the position of the locking pin. The grooves or bores on the locking pin, in effect, constitute flow-transfer channels via which the two sections of the pressure medium conduit are fluidically connected to each other.
It is further proposed that the first switchable valve device include at least one spring-loaded linearly displaceable valve function pin. In contrast to the locking pins, the valve function pin serves only to short-circuit the working chambers and is spring-loaded toward an engaged position in the locking slot, in which it establishes a fluid connection between the working chambers of different directions of action. It is only after pressurizing the locking slot that the valve function pin is urged out of the locking slot into an out-of-engagement position in which the fluid connection between the working chambers of different directions of action is interrupted and the short-circuit is removed.
It is further proposed that at least one of the vanes have provided therein a second switchable valve device which allows the flow of pressure medium to the check valves to be selectively blocked or enabled, depending on the position of the second valve device. The solution proposed herein makes it possible to, in effect, deactivate the check valves, so that, during normal operation, the pressure medium is prevented from being transferred between the working chambers and the phasing accuracy is further improved.
It is also proposed that the rotor hub have provided therein one or more partial ring-shaped or ring-shaped pressure medium conduits into which open at least some of the pressure medium conduits leading to the working chambers, and that the first switchable valve device be disposed in a pressure medium conduit that fluidically connects the two partial ring-shaped or ring-shaped pressure medium conduits. The solution proposed herein makes it possible to achieve a readily producible routing configuration of the pressure medium conduits, which in particular allows a plurality of working chambers of one direction of action to be short-circuited to a group of working chambers of a different direction of action via a single switchable valve device.